1. Field of the Invention
The present invention relates to a medical image processing apparatuses, an X-ray computed tomography (CT) apparatus, a magnetic resonance imaging (MRI) apparatus, an ultrasound diagnostic imaging apparatus, and a medical image processing method used to examine hepatic functions with perfusion technique.
2. Description of the Related Art
As an example of techniques used to examine hepatic functions with an X-ray CT apparatus, there is a CT-perfusion technique which involves quantifying parameters of a hepatic blood flow using an iodine contrast agent as a tracer. Examples of images obtained by calculation based on the CT-perfusion technique are shown in FIG. 3.
As a hepatocellular cancer progresses, a hepatic blood flow slows down and a hepatic arterial fraction (i.e., hepatic arterial blood volume/(hepatic arterial blood volume+portal venous blood volume)) increases, as shown in FIG. 4. The increase in hepatic arterial fraction indicates that although a decrease in portal venous blood volume leads to a decrease in total hepatic blood volume, the decrease is compensated for by the increase in blood volume in the hepatic artery serving as a feeding blood vessel, the increase being caused by the effect of the hepatocellular cancer.
Nutrients are supplied to normal hepatic cells at a hepatic-arterial-blood-volume to portal-venous-blood-volume ratio of 2:8, that is, at a hepatic arterial fraction of 20%. However, it has been reported that in early stages of cancer, such as a regenerative nodule stage and an adenoma stage, a portal venous blood volume and a hepatic arterial blood volume decrease (ischemia occurs) in the affected area, and as a stage (degree of cancer progression) progresses and a plethoric hepatocellular cancer stage approaches, the hepatic arterial blood volume increases while the portal venous blood volume decreases in the affected area (see, e.g., a following Document 1).
Document 1: Makiko Hayashi, Osamu Matsui, et al. “Correlation Between the Blood Supply and Grade of Malignancy of Hepatocellular Nodules Associated with Liver Cirrhosis: Evaluation by CT During Intraarterial Injection of Contrast Medium” AJR: 172, April 1999: 969-976
Thus, since the hepatic arterial fraction increases as the plethoric hepatocellular cancer stage approaches, it is possible to diagnose a cancer in advanced stages, such as an early liver cancer stage and a plethoric hepatocellular cancer stage, because an apparent increase in hepatic arterial fraction can be observed.
However, in the early stages, such as the regenerative nodule stage and the adenoma stage, since there is an occurrence of ischemia in which the portal venous blood volume and the hepatic arterial blood volume decrease at substantially the same rate, the hepatic arterial fraction tends to be determined to be 20%, which is the same as that in normal (unaffected) areas. As a result, it is difficult to make early detection of hepatic tumor and stage determination of cancer in early stages.